44 lines
1.5 KiB
Plaintext
44 lines
1.5 KiB
Plaintext
Power Management Interface
|
|
|
|
|
|
The power management subsystem provides a unified sysfs interface to
|
|
userspace, regardless of what architecture or platform one is
|
|
running. The interface exists in /sys/power/ directory (assuming sysfs
|
|
is mounted at /sys).
|
|
|
|
/sys/power/state controls system power state. Reading from this file
|
|
returns what states are supported, which is hard-coded to 'standby'
|
|
(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
|
|
(Suspend-to-Disk).
|
|
|
|
Writing to this file one of those strings causes the system to
|
|
transition into that state. Please see the file
|
|
Documentation/power/states.txt for a description of each of those
|
|
states.
|
|
|
|
|
|
/sys/power/disk controls the operating mode of the suspend-to-disk
|
|
mechanism. Suspend-to-disk can be handled in several ways. The
|
|
greatest distinction is who writes memory to disk - the firmware or
|
|
the kernel. If the firmware does it, we assume that it also handles
|
|
suspending the system.
|
|
|
|
If the kernel does it, then we have three options for putting the system
|
|
to sleep - using the platform driver (e.g. ACPI or other PM
|
|
registers), powering off the system or rebooting the system (for
|
|
testing). The system will support either 'firmware' or 'platform', and
|
|
that is known a priori. But, the user may choose 'shutdown' or
|
|
'reboot' as alternatives.
|
|
|
|
Reading from this file will display what the mode is currently set
|
|
to. Writing to this file will accept one of
|
|
|
|
'firmware'
|
|
'platform'
|
|
'shutdown'
|
|
'reboot'
|
|
|
|
It will only change to 'firmware' or 'platform' if the system supports
|
|
it.
|
|
|